LT1 with boost.

[Dave Zug]

----- Original Message -----
From: Dave Plummer <davepl at MICROSOFT.com>
To: <diy_efi at diy-efi.org>; <gmecm at diy-efi.org>
Sent: Tuesday, February 01, 2000 1:24 PM
Subject: RE: LT1 with boost.


> Two questions, then:
>
> 1) Why is an FMU required on a MAF car at all, then?  Shouldn't it just
see
> the amount of air going through and add the right amount of fuel
> "automagically"?
>

when the air hits 255 g/s to the MAF - it can't tell how much mass-air its
getting aboe that. it will be in open loop at that point, NOT using the o2.
the FMY fine tunes what the ECM can't see. an illustration would be using
30# of boost on a 500CI engine.. the MAF would see 255 at about 2400 rpm -
the RPM based fuel adder in the ECM would try to help byt the cal is
probably from a 350 engine and it will fall short.  mostly I guess FMU's are
for cars with no chip mods and major air / fuel mods like blower.

> 2) Are there MAF <-> FUEL tables anywhere in the PCM?  I've never seen
them
> in the '94/95 LT1 pcms.  Or is it just a formula?
>

ooh thats right - dont the PCM's calc the base inj-pw constantly?? help
again ;-}

> - Dave
>
> > > 1.  VE is only used for backup mode if the MAF fails, so
> > forget it for
> > now.
> > > 2.  All fueling is calculated from MAF (until you max out.
> > . .335 grams
> > impala, 471 grams F/Y car)
> > > 3.  The PE/RPM table is a % change to base A/F ratio with
> > higher numbers
> > >     making the mixture richer.  If you max the sensor, you
> > just have to go
> > 'over-rich'
> > >     in the table at that RPM point.  Easy to do, no
> > problem, works fine.
> > > 4.  If you have the reprogramming capabilities (a friends
> > shop, in my
> > case) FMU's suck.
> --------------------------------------------------------------------------
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